In general, emulsions can be formed by dispersing liquid droplets (dispersed phase) in another immiscible or partly miscible liquid (continuous phase). Two liquids can form different types of emulsions. For example, oil and water can form, an oil-in-water emulsion, wherein the oil is the dispersed phase, and water is the continuous phase. Alternatively, they can form a water-in-oil emulsion, wherein water is the dispersed phase and oil is the continuous phase. Multiple emulsions are also possible, including a “water-in-oil-in-water” emulsion and an “oil-in-water-in-oil” emulsion.
Emulsions can be formed either by mechanical disintegration of bulk liquid into the fine droplets forming the disperse phase, or by phase-inversion technique (where the dispersed phases and continuous phases of the system are exchanged i.e. oil in water emulsion, may be reverted to a water in oil and vice versa). Other techniques rely on using flow devices where the dispersed phase is injected into the continuous phase through membranes or through nozzles/microchannels embedded in substrates.